This application claims the benefit of Korean Application No. 2002-7026, filed Feb. 7, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to a developer unit for a wet-type color image forming apparatus, having a metering roller and using a high-concentration liquid developing agent.
2. Description of the Related Art
An image forming apparatus, such as a printer, photocopier, or scanner, includes an electrostatic latent image formation unit, a developer unit to develop the electrostatic latent image, and a transfer unit to transfer the developed image to a printing paper.
A conventional wet-type color image forming apparatus having the above structure is shown in FIG. 1. In FIG. 1, reference numerals 100, 102, 104, and 106 denote first through fourth photoreceptors in which electrostatic latent images to be developed into color images of cyan (C), magenta (M), yellow (Y), and black (K) are formed, respectively. Reference numerals 110, 112, 114, and 116 denote first through fourth cleaning blades that respectively clean the first through fourth photoreceptors 100, 102, 104, and 106. Reference numeral 130 denotes a transfer belt to which the developed images are sequentially transferred from the first through fourth photoreceptors 100, 102, 104, and 106, thereby forming an overlapped color image to be transferred to a paper 90. A plurality of rollers 132, 134, 138, 140, 142, and 144, which have different functions, are arranged inside the transfer belt 130 and support the transfer belt 130 in a predetermined tensioned state. In particular, reference numeral 132 denotes a driver roller that rotates the transfer belt 130, reference numeral 134 denotes a backup roller that supports the transfer belt 130 against a transfer-to-paper roller 136 while the developed color image is transferred to a printing paper 90 and to which a voltage required for color image transfer is applied. Reference numerals 138, 140, 142, and 144 denote first through fourth transfer rollers that contact the respective first through fourth photoreceptors 100, 102, 104, and 106, with the transfer belt 130 therebetween. The transfer rollers 138, 140, 142 and 144 transfer the developed images from the respective first through fourth photoreceptors 100, 102, 104, and 106 to the transfer belt 130. Since the developed images on the first through fourth photoreceptors 100, 102, 104, and 106 are charged, the first through fourth transfer rollers 138, 140, 142, and 144 may be charged to have a polarity opposite to a polarity of the first through fourth photoreceptors 100, 102, 104, and 106, respectively.
Although not illustrated in FIG. 1, the first through fourth transfer rollers 138, 140, 142, and 144 are connected to separate power sources. Once a color image is transferred to the transfer belt 130, subsequently the color image is transferred to the printing paper 90. A voltage having a polarity opposite to the polarity of the voltage that is applied to the first through fourth transfer rollers 138, 140, 142, and 144 must be applied to the backup roller 134. Although not illustrated in FIG. 1, the backup roller 134 is also connected to a power source.
Reference numerals 120, 122, 124, and 126 denote first through fourth developers, respectively, which constitute a single developer unit to develop the electrostatic latent images. The first through fourth developers 120, 122124, and 126 supply ink of cyan, magenta, yellow, and black to the first through fourth photoreceptors 100, 102, 104, and 106, respectively, in order to develop the electrostatic latent images on the respective first through fourth photoreceptors 100, 102, 104, and 106. The first through fourth developers 120, 122, 124, and 126 have the same internal structure. The ink of different colors is supplied to the first through fourth developers 120, 122, 124, and 126 by respective first through fourth developing rollers 120a, 122a, 124a, and 126a, which are attached to the respective first through fourth developers 120, 122, 124, and 126.
Referring to FIG. 2, the first developer 120 includes a developer bath 120c filled with ink 120b to a predetermined height, the first developing roller 120a, which is partially immersed in the ink 120b and contacts the first photoreceptor 100, and a cleaning roller 120d, which is immersed in the ink 120b and removes the unnecessary residual ink from the surface of the first developing roller 120a. The first developer 120 further includes an ink depositing roller 120e, which is immersed in the ink 120b and electrically deposits the ink 120b onto the surface of the first developing roller 120a from which the unnecessary residual ink has been removed, and a metering blade 120f, which is separated by a predetermined distance above the ink 120b and appropriately controls the thickness and concentration of the ink layer deposited on the first developing roller 120a by the ink depositing roller 120e. The ink depositing roller 120e is connected to a power source S to be able to electrically deposit the ink 120b on the first developing roller 120a. As a predetermined voltage is applied to the ink depositing roller 120e from the power source S, the ink 120b is electrically charged to be deposited onto the first developing roller 120a. 
As described above, since the developer unit of the conventional wet-type color image forming apparatus includes the metering blade installed around the developing roller, a high-concentration ink of about 3-18% or a constant amount of ink can be supplied to the transfer roller regardless of changes in the concentration of the ink. This is done so that images can be uniformly developed.
However, when toner particles are back-plated onto the surface of the developing roller, uniform development cannot be achieved. In other words, when toner particles are stuck in the space between the metering blade and the developing roller, when toner particles that have lost magneticity form clusters, when impurities are generated, or when the metering blade has a defect at its edge, the ink may be applied partially to the developing roller or in a low concentration. The non-uniform ink layer on the developing roller is transferred to the photoreceptor. As a result, a uniform, perfect color image, as shown in FIG. 3, cannot be achieved. Instead, the final color image may have a stripe pattern P, as shown in FIG. 4.
Accordingly, it is an aspect of the present invention to provide a developer unit for a wet-type color image forming apparatus, capable of preventing image quality degradation due to toner impurities adhered to a developing roller or due to a defect in a metering roller.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and/or other aspects of the present invention may be achieved by providing a developer unit for a wet-type color image forming apparatus to develop an electrostatic latent image formed on a photoreceptor, including a developer bath filled with a liquid developing agent; a developing roller to develop the electrostatic latent image to correspond to an original image by supplying the liquid developing agent while being partially immersed in the liquid developing agent; a cleaning roller to clean a surface of the developing roller; a depositing roller to deposit the liquid developing agent onto the cleaned surface of the developing roller; a metering roller to adjust a thickness and a concentration of the liquid developing agent deposited onto the surface of the developing roller to suitable levels; and a developer cartridge to supply the liquid developing agent into the developer bath.
An initial concentration of the liquid developing agent may be 2% or more, and more specifically, may be in the range of 2-40%. In the developer unit, the metering roller may be driven by the developing roller or a separate driving source. A power source may be connected to the metering roller.
When the developer unit for the wet color image forming apparatus according to the embodiment of the present invention is used, the metering roller continuously rotates rather than being fixed, and attracts back-plated toner particles or impurities so that no toner particles or impurities are stuck to the space between the developing roller and the metering roller. As a result, a developing agent layer deposited on the developing roller can be protected from being scratched by the back-plated toner particles or impurities, and thus no unwanted stripe pattern appears on the final image.
The foregoing and/or other aspects are achieved by providing an apparatus, including a photoreceptor having an electrostatic latent image thereon; a developing roller to develop the electrostatic latent image with a developer comprised of particles; and a metering roller to continuously rotate to adjust a thickness of the developer on the developing roller. The developing roller may be partially immersed in the developer.